Pressure-induced enhancement of the critical current density in superconducting YBa2Cu3Ox bicrystalline rings

The dependence of the critical current density Jc T on hydrostatic He-gas pressure to 0.6 GPa is determined for nearly optimally doped and strongly underdoped melt-textured YBa2Cu3Ox bicrystalline rings containing single 001 -tilt grain boundaries GBs with mismatch angles from 0° to 31°. For all samples with 0°, Jc is found to increase rapidly under pressure, the rate of increase lying predominantly in the range +20 to +50 % GPa−1. Within a simple tunneling model, this rate of increase is far too large to be accounted for by a decrease in the GB width W alone. Large oxygen relaxation phenomena in the GB are observed for all rings with finite , particularly if they are underdoped. A diagnostic method is introduced pressure-induced Jc relaxation which reveals a significant concentration of vacant oxygen sites in the GB region. A concerted effort to fill such sites with oxygen anions, as well as to chemically compress the GB itself, should lead to significant enhancements in Jc under ambient conditions.